U.S. Pat. No. 3,288,965 describes a residential type circuit breaker assembly containing a movable contact assembly, an operating spring, a releasable member called a cradle and a latch member. The metallic cradle tip is held by the metallic latch member until the latch is moved from under the cradle by conventional thermal or magnetic means to release the cradle and trip the breaker. The operating spring directly connects the movable contact assembly to the metallic cradle and its tip rests directly upon the metallic latch. There is no intentional connection of the latch to the load terminal and hence no intentional current flow through the cradle to the latch engaging surface.
When the breaker is subjected to short circuit currents, the contacts are separated by magnetic forces before the latch can be disengaged from the cradle by the conventional thermal tripping means. An unintentional circuit between the cradle and the latch roughens the engaging surfaces and greatly increases the force required to trip the breaker during subsequent operations. One possible explanation being that the cradle is electrically connected to the movable contact arm by the operating spring. An insulator such as that described within U.S. Pat. No. 2,844,689 is used within some circuit breaker designs to deter a conduction path from the movable contact arm directly to the latching tip of the cradle and to the engaging surface of the latch.
U.S. Pat. No. 4,481,491 describes an insulated latching arrangement in the form of an apertured fiber insulating plate that receives the end of the cradle without allowing electrical contact between the end of the cradle and the latch. It has been determined, however, that long term movement of the metallic cradle tip over the surface of the fiber insulating plate could cause slight erosion of the fiber material. The latching arrangement also includes a tolerance take-up spring that interacts with the circuit breaker trip bar and the circuit breaker cradle to ensure that the cradle tip is at its lowest possible position after responding to an overcurrent trip function.
U.S. Pat. Nos. 3,246,098 and 3,467,920 both describe a z-shaped latch plate within the latch assembly arranged for supporting the cradle tip during quiescent circuit current conditions.
Applicants have determined that a common metal insert attached within the latch assembly, by means of an insulative plate, will allow the cradle tip to interact with the metal insert surface at one end while multi-functionally providing tolerance take-up function at an opposite end.
Accordingly, one purpose of the invention is to provide an insulated armature latch assembly with metal-to-metal contact between the cradle tip and the latching surface, while providing tolerance take-up function without requiring an additional tolerance take-up spring.